1. Field of the Invention
This invention relates to a semiconductor memory device and a control method for the semiconductor memory device. More particularly, this invention relates to a nonvolatile semiconductor memory device including MOS transistors, each having a floating gate and a control gate.
2. Description of the Related Art
NOR and NAND flash memories have been widely used as nonvolatile semiconductor memories.
In recent years, a flash memory combining the features of both the NOR and the NAND flash memory has been proposed in, for example, Wei-Hua Liu, “A 2-Transistor Source-select (2TS) Flash EEPROM for 1.8-V-Only Application,” Non-Volatile Semiconductor Memory Workshop 4.1, 1997. A flash memory of this type has memory cells, each including two MOS transistors (hereinafter, referred to as a 2Tr flash memory). In a memory cell of a 2Tr flash memory, one MOS transistor functioning as a nonvolatile memory section has a structure including a control gate and a floating gate and is connected to a bit line. The other MOS transistor, which is connected to a source line, is used to select the memory cell.
Such a nonvolatile semiconductor memory device as the 2Tr flash memory described above has a write circuit for holding write data. A write circuit provided in a semiconductor memory has been disclosed in Jpn. Pat. Appln. KOKAI 9-180453. The size of the write circuit is relatively large and therefore miniaturization of LSI is difficult.